Metallic gasket

ABSTRACT

A metallic gasket comprising a base plate having a first thickness-increased portion  3  formed at a peripheral edge on a combustion chamber opening  3  side of a base plate, and a first seal line SL 1  and a second seal line SL 2  arranged on the outer side of said first thickness-increased portion  3 . No openings other than a cooling water hole  8  exist between said two seal lines. Beads formed along said seal lines SL  1  and SL 2  each consist of a convex metal bead raised only upward from an upper surface of said base plate and a rubber bead made of an elastic sealing material fixed to a convex portion and a concave portion of said metal bead. This structure of said metallic gasket can improve a processing accuracy of said metal bead and also enhance cooling effects on said metallic gasket itself and said joint surfaces of an engine, between which said metallic gasket is disposed.

TECHNICAL FIELD

[0001] The present invention relates to a metallic gasket and moreparticularly to a metallic gasket which is sandwiched in a joint betweenthe joint surfaces of a cylinder block and a cylinder head of awater-cooled internal combustion engine, and which is capable ofimproving the cooling effect of the joint and the gasket itself.

BACKGROUND ART

[0002] Among conventional metallic gaskets aimed at improving thecooling effects of the parts between which a metallic gasket issandwiched, there is one which is described in Japanese Patent Laid-OpenNo. 60-3465.

[0003] As shown in FIGS. 21 and 22, this metallic gasket comprises abase plate 50 made of a thin, high-rigidity, elastic metal plate havinga first metal bead 52 formed along a seal line SL1 encircling the innerperipheral edge of each combustion chamber opening 51. In the base plate50, on the outer side of the first metal bead 52, a second metal bead 55is formed along a seal line SL2 encircling cooling water holes 53 butseparating and not encircling bolt holes 54. Reference numeral 56denotes an oil hole, and a third seal line SL3 is formed encircling theinner peripheral edge of the oil hole 56.

[0004] When the metallic gasket is mounted at the joint between thejoint surface of a cylinder block 60 and the joint surface of a cylinderhead 61 and fastened with bolts, the metal beads 52, 55 are elasticallydeformed according to a fastening force, a combustion gas of thecombustion chamber bore 51 is line-sealed by the first metal bead 52 anda gap space S at a minute height, to which only the cooling water holes53 are open, is formed between the two metal beads 52, 55. Cooling wateris pressure-fed through the cooling water holes 53 into the gap space Swhen the engine is running, and as a result of cooling watercirculation, the joint surfaces and the metallic gasket itself arecooled. Also by the pumping action of vibration amplitude caused byexplosion of the combustion gas, the flow of cooling water to the gapspace S is promoted.

[0005] The minute gap of the gap space S is formed by a balance of theaxial tension of the clamping bolts of the engine with the urging forceof the metal beads 52, 55 that resist the fastening. Since a line sealby metal is applied, it is necessary to set a high gasket factor tosecure a desired sealing property, so that the axial tension of thebolts must be set on a higher side, and the gap tends to become small.

[0006] Further, the cubical expansion of the engine occurs by the heatof engine operation, increasing the fastening pressure, and as thetemperature rises, the above-mentioned gap decreases. Progresses havebeen made in reductions in size and weight, technical sophistication,and energy saving of the engine, and aluminum has come to be used ingreater quantities as material for the engines. As a result of increasedexpansion coefficient by a difference of materials, there is a tendencythat it is becoming difficult to secure the above-mentioned gap.

[0007] Further, in the bead structure of the above-mentioned gasket, asdescribed above, the metal beads 52, 55 formed in the base plate 50 needto generate a high surface pressure. Therefore, it is necessary to adopta material of high hardness, and in hard materials, internal stressconcentrates in the portions of bending radius of the metal beads 52,55, and when subjected to repetitive stress by vibration amplitude, theyare liable to fatigue failure, and gasket lifetime is shortened.

[0008] Supposing an engine is made by aluminum, casting of aluminum isdifficult and blowholes occur in casting. Therefore, when processing thejoint surfaces, adjacent blowholes on the joint surfaces are sometimesconnected. At this time, the conventional beads 52, 55 are for linesealing and come into metal-to-metal contact with the joint surfaces,and therefore the blowholes may stretch, running across the line-sealedbead line, or the seal line may be displaced during operation due to anexpansion difference between materials of the gasket and the engine,resulting in the beads 52, 55 being located on the blowholes, increasingchances of water leakage. An aluminum-made engine is liable to dents intransit. Those dents may give rise to the above-mentioned phenomena.

[0009] Further, since the base plate 50 needs to be formed by a materialof high hardness, it is difficult to improve the processing accuracy ofthe metal beads 52, 55 formed by bending the base plate 50.

[0010] Among other conventional metallic gaskets, there is one which isdisclosed in Japanese Patent Laid-Open No. 2001-173791.

[0011] As shown in FIG. 23, this metallic gasket comprises two baseplates 50. In other words, a thickness-increased portion 52 is formed atthe inner peripheral end of the combustion chamber opening 51 side ofthe thicker base plate (the upper base plate) out of the two base plates50, convex beads 53 are formed on the base plates 50, each on the outerside of the thickness-increased portion 52 and at a height higher thanthe thickness of the thickness-increased portion 52, and the two baseplates 50 are laminated in such a way that the convex sides of thebase-plate beads 53 face each other. Further, an elastic sealingmaterial 54 is filled in the outside-facing concave portions of themetal bead 53.

[0012] The metallic gasket is disposed between the opposing jointsurfaces of the cylinder head and the cylinder block, and when they arefastened together, the base-plate beads 53 are compressed and deformeduntil the thickness-increased portion abuts on the opposite base plateat the peripheral edge of the combustion chamber opening, concurrentlywith which, the elastic sealing material parts 54 filled in the concaveportion are compressed and deformed, and consequently a combustion gas,oil, and cooling water are sealed by a sealing pressure from a combinedspring including the spring force of the base-plate beads 53 and thespring force of the elastic sealing material parts 54. Needless to say,some of the conventional metal beads have no elastic sealing materialfilled in their concave portion and some conventional metal beads areformed by a single piece of base plate.

[0013] In this conventional metallic gasket, when the base-plate beads53 and the elastic sealing material parts 54 are deformed when the boltsare tightened, they cooperate to generate a resilience to therebygenerate a required sealing pressure along the seal lines.

[0014] However, when the base plate 50 is formed of metal plate of lowhardness with a view to preventing fatigue failure of the base-platebeads 53 and reducing production cost, in the above-mentioned metallicgasket, when the bolts are fastened and the elastic sealing material 54in the concave portion is deformed under compression, an external forceacts to deform the base plate 50 and the base-plate beads 53 to warp inthe through-thickness direction. When the base plate 50 is made of metalof low hardness as mentioned above, the bead shape-preserving power islow and the base plate deformation resistance is weak, so that thesealing property is reduced accordingly.

[0015] By repeated load by repetition of operation and stoppage of theengine, after a long period of use, problems arise, such as a decreasein axial tension of the clamping bolts, changes with time of thebase-plate bead 53 on the base plate 50, or deterioration in the elasticsealing material 54 of the concave portion of the bead; therefore, theseal surface pressure is likely to drop. Such problems tend to come upparticularly at overhanging parts on the outer side of the clampingbolts.

[0016] When the elastic sealing material 54 is formed by baking in theconcave portions of the base plates, even if the elastic sealingmaterial 54 at high temperature is filled in the concave portions, itchanges in volume by an amount of thermal expansion during subsequentopen cooling, the center portion of the elastic sealing material 54where the thickness is at its highest contracts by an amount of thermalshrinkage. This is disadvantageous when the surface pressure decreasesas described above. Such a phenomenon as this seems to be likely tooccur particularly when the gasket is mounted in the engine which hasbeen assembled with a weak fastening axial tension.

DISCLOSURE OF THE INVENTION

[0017] The present invention has been made with the above problems inmind, and has as its task to provide a metallic gasket capable ofimproving the processing accuracy of metal beads, and enhancing thecooling effects on the metallic gasket itself and the joint surfaces inwhich the metallic gasket is mounted.

[0018] To solve the above problems, the invention set forth in claim 1relates to a metallic gasket comprising a base plate made of a thinmetal plate, the base plate having at least a combustion chamber openingand a cooling water hole, and having a first thickness-increased portionmade of metal and increased in thickness and encircling a peripheralportion of the combustion chamber opening, a first bead formed on theouter side of the first thickness-increased portion of the base plate ina manner to endlessly encircle the combustion chamber opening, and asecond bead formed on the outer side of the first bead in a manner toendlessly encircle the combustion chamber opening and the cooling waterhole, wherein in a region of the base plate between the first bead andthe second bead, there are no holes other than the cooling water hole,and each of the first and second beads is a composite bead of a metalbead and a rubber bead, wherein the metal bead is formed only on onesurface of the base plate by bending the base plate in athrough-thickness direction to create a convex portion higher than theheight of the first thickness-increased portion, wherein the rubber beadis formed of an elastic sealing material fixed to the convex portionside surface of the metal bead and filled in a concave portion on thereverse side of the convex portion and the rubber bead is compressed anddeformed in the through-thickness direction in cooperation with thedeformation of the metal bead, and wherein the elastic sealing materialon the surface of the convex portion side is fixed at least to thesurface of the convex portion of the metal bead and is arranged to havea height equal or substantially equal to the height of the metal bead.

[0019] Incidentally, it is desirable to limit the largest width of therubber bead on the convex portion side within 1.5 times the width of themetal bead with the exception of the bolted portions which are subjectedto a large pressure. It is necessary to apply more load to the baseplate where the rubber bead has a larger width. From a viewpoint ofinhibiting an increase in load, it is desirable to limit the width ofthe bead of an elastic sealing material within 1.5 times the width ofthe metal bead as mentioned above. This does not apply to where largeload is to be applied locally.

[0020] According to the present invention, the first thickness-increasedportion made of metal receives most of the fastening surface pressureand seals a combustion gas of high pressure. Cooling water that flowsthrough the cooling water hole into and out of a gap space between thefirst bead and the second bead is sealed by a composite spring force ofa spring force of the metal bead higher than the height of thethickness-increased portion and a spring force by the elasticdeformation of the rubber bead formed on both surfaces of the metalbead.

[0021] At this time, since the compression-deformed amount of the beadsis regulated by the first thickness-increased portion, a gap space by agap greater than before is formed between the first bead and the secondbead, and consequently the cooling effect on the metal bead and so on isincreased.

[0022] At this time, the bead according to the present invention appliesa seal by a composite spring force of the metal bead and the rubberbead, and since the seal surface of the beads that contact the opposingjoint surface is formed by an elastic sealing material, the gasketfactor is small, so that the joint can be sealed with a low surfacepressure and no problem arises even if the compression-deformed amountis regulated as mentioned above.

[0023] Because the sealing surface is formed by the elastic sealingmaterial, even if there are blowholes on the joint surfaces, asatisfactory sealing can be achieved to prevent water leakage.

[0024] The rubber bead is soft and adapts itself to the joint surfacesand is capable of accommodating the processed surface roughness andsatisfactorily sealing the flaws that occur in transit.

[0025] Because a small gasket factor can be adopted for the bead asmentioned above, the hardness of the base plate used for metal beads canbe set at a low value. For example, with an intention of providinginexpensive gaskets, plated soft steel may be adopted instead ofhigh-hardness stainless steel. The amount of elastic sealing materialused is small because it is used only on the upper and lower surfaces ofthe bead lines for sealing.

[0026] The metal beads are required only slightly higher than the heightof the first thickness-increased portion, and the height of the rubberbeads is set so as to be equal or slightly higher than the height of themetal beads in designing the mold, and therefore the processing accuracyis stable. If the height of the metal beads is 30% higher than the firstthickness-increased portion, the elastic sealing material does notsuffer deformation fracture, generated load is a composite force of themetal beads of soft steel and the soft rubber beads and is therefore notstrong, and there is not such a large loss of load as to affects thesealing against the combustion gas pressure.

[0027] [Cl-2]

[0028] The invention set forth in claim 2 is based on claim 1 and ischaracterized in that a second thickness-increased portion is providedat an outer peripheral edge of the base plate.

[0029] According to the present invention, most of the fastening surfacepressure is received by the two thickness-increased portions made ofmetal. In the additional presence of the thickness-increased portion atthe outer peripheral edge of the base plate, the compression-deformedamount of the beads can be set stably at a specified value.

[0030] [Cl-3]

[0031] The invention set forth in claim 3 is based on claim 2 and ischaracterized in that to equalize the surface pressure when the gasketis mounted between the joint surfaces, the height of the firstthickness-increased portion is varied partly and that the height of thesecond thickness-increased portion is lower than the lowest height ofthe first thickness-increased portion.

[0032] According to the present invention, as a result of the sealingpressure being equalized by the first thickness-increased portion, thebolt fastening force can be utilized efficiently. Equalizing the sealingpressure in the circumferential direction at the inner peripheralportion of the combustion chamber opening means that the pressure tothat portion of the joint surface which is the first thickness-increasedportion at the inner peripheral portion of the combustion chamberopening is also equalized circumferentially, thereby preventing theshape distortion of the bore on the joint surface by the sealingpressure at the first thickness-increased portion. If the shape of theopening on the joint surface is deformed, or distorted, this leads topower loss or oil consumption increase.

[0033] In the first and second thickness-increased portions that receivea greater part of the bolt fastening force, by setting the secondthickness-increased portion to a relatively lower thickness, it becomespossible for the largest load to be applied to the firstthickness-increased portion, thereby generating a high sealing pressure.

[0034] [Cl-4]

[0035] The invention set forth in claim 4 is based on claim 3 and ischaracterized in that the first thickness-increased portion is formed byfolding back the peripheral edge on the combustion chamber opening sideof the base plate, and a shim is fitted into the folded portion tothereby adjust the height of the first thickness-increased portion.

[0036] According to the present invention, it becomes possible to lowerthe hardness of the base plate as described above, and therefore formingthe first thickness-increased portion by bending becomes easier and itbecomes possible to adjust the height of the first thickness-increasedportion by means of a shim.

[0037] When the second thickness-increased portion is formed by bending,by the above mentioned insertion of a shim, it becomes possible to setthe second thickness-increased portion to a lower height than the heightof the first thickness-increased portion without subjecting the secondthickness-increased portion to forging.

[0038] [Cl-5]

[0039] The invention set forth in claim 5 is based on one of claims 1 to4 and is characterized in that the first thickness-increased portion isformed by folding back the peripheral end on the combustion chamberopening side of the base plate, and a leaf spring for spring action inthe through-thickness direction is inserted in the folded portion.

[0040] According to the present invention, by imparting elasticity bythe leaf spring to the whole or a part of the first thickness-increasedportion, the surface pressure in the circumferential direction can beequalized easily, and by providing the first thickness-increased portionwith the spring, the first thickness-increased portion can follow afterthe thermal deformation that occurs during engine operation, andconsequently the surface pressure equalization takes places in the firstthickness-increased portion in a manner to follow after the thermaldeformation.

[0041] [Cl-6]

[0042] The invention set forth in claim 6 is based on one of claims 1 to4 and is characterized in that by partly varying at least one of theheight of protrusion and the width of the beads in the extendingdirection thereof, the sealing surface pressure by the beads isequalized in the extending direction thereof.

[0043] [Cl-7]

[0044] The invention set forth in claim 7 is based on one of claims 1 to4 and is characterized in that a thin corrosion-resistant film is fixedto that portion of the base plate located between the first bead and thesecond bead and at least on the surface of the convex portion side ofthe metal beads on the base plate.

[0045] [Cl-8]

[0046] The invention set forth in claim 8 is based on one of claims 1 to4 and is characterized in that one or not less than two seal lines arearranged on at least one of the surface of the elastic sealing materialfixed to the surface of the convex portion side and the surface of theelastic sealing material filled in the concave portion, the sealingmaterial being used to form the rubber beads.

[0047] [Cl-9]

[0048] The invention set forth in claim 9 is based on one of claims 1 to4 and is characterized in that one line or not less than two lines ofprotrusions are provided where the sealing pressure is relatively low onat least one of the surface of the elastic sealing material fixed to thesurface of the convex portion side and the surface of the sealingmaterial filled in the concave portion of the base plate, the sealingmaterial being used to constitute the rubber beads.

[0049] [Cl-10]

[0050] The invention set forth in claim 10 is based on claim 8 and ischaracterized in that in the above-mentioned lines of protrusions, atleast one of the height of protrusion and the width in the extendingdirection thereof is varied according to the sealing pressure at formedpositions the protrusions, and at least one of the protrusion height andthe width is set at a larger value where the sealing pressure is lower.

[0051] [Cl-11]

[0052] The invention set forth in claim 11 is based on claim 8 and ischaracterized in that a plurality of protrusions are provided on atleast one of the surface of elastic sealing material fixed to thesurface of the convex portion side and the surface of the elasticsealing material filled in the concave portion of the beads, and in theplurality of protrusions, at least one of an area per height ofprotrusion and a unit length is varied according to the sealing pressureat formed positions of protrusions.

[0053] [Cl-12]

[0054] The invention set forth in claim 12 is based on one of claims 8,10 and 11, wherein a plurality of base plates are stacked in amultilayered structure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055]FIG. 1 is plan view for explaining a metallic gasket according toa first embodiment of the present invention.

[0056]FIG. 2 is a sectional view taken along the line A-A in FIG. 1.

[0057]FIG. 3 is a sectional view taken along the line B-B in FIG. 1.

[0058]FIG. 4 is a sectional view for explaining another mode ofembodying a first thickness-increased portion.

[0059]FIG. 5 is a sectional view for explaining yet another mode ofembodying the first thickness-increased portion.

[0060]FIG. 6 is a diagram for explaining another mode of embodying abead.

[0061]FIG. 7 is a sectional view for explaining a still other mode ofembodying the first thickness-increased portion.

[0062]FIG. 8 is a sectional view showing a bead according to a secondembodiment of the present invention.

[0063]FIG. 9 is another example of protrusion formation.

[0064]FIG. 10 is a still other example of protrusion formation.

[0065]FIG. 11 is a yet further example of protrusion formation.

[0066]FIG. 12 is an additional example of protrusion formation.

[0067]FIG. 13 is a still further example of protrusion formation.

[0068]FIG. 14 is another example of protrusion formation.

[0069]FIG. 15 is yet another example of protrusion formation.

[0070]FIG. 16 is a still other example of protrusion formation.

[0071]FIG. 17 is a further example of protrusion formation.

[0072]FIG. 18 is an example that the base-plate bead is a half bead.

[0073]FIG. 19 is another example that the base-plate bead is a halfbead.

[0074]FIG. 20 is a modification of a second elastic sealing material.

[0075]FIG. 21 is a plan view for explaining a conventional metallicgasket.

[0076]FIG. 22 is a sectional view taken along the line D-D in FIG. 21.

[0077]FIG. 23 is a diagram for explaining a conventional metal bead.

BEST MODE FOR CARRYING OUT THE INVENTION

[0078] A first embodiment of the present invention will be describedwith reference to the drawings.

[0079]FIG. 1 is a plan view for explaining a metallic gasket accordingto the first embodiment of the present invention. FIG. 2 is a sectionalview taken along the line A-A in FIG. 1. FIG. 3 is a sectional viewtaken along the line B-B in FIG. 3.

[0080] Description will next be made of the structure of the metallicgasket according to the first embodiment.

[0081] A metallic gasket 1 according to the first embodiment is anembodiment of a cylinder head gasket for an internal combustion engine.A base plate 20 of the metallic gasket 1 comprises thin metal plate,such stainless steel plate, soft steel plate, or steel plate. Here, thefirst embodiment will be described on the assumption that soft steelplate is used as a material for the base plate 20 with a view toproviding a less expensive product.

[0082] As shown in FIG. 1, the base plate 20 is provided with aplurality of combustion chamber openings 2 aligned to each other in thelongitudinal direction, and a first thickness-increased portion 3 isformed by upwardly folding back the whole of the inner peripheral edgeon the each combustion chamber opening 2 side of the base plate. Theheight of the first thickness-increased portion 3 is varied in itsextending direction, such as by lowering the height at positions nearbolt holes, to thereby equalize the surface pressure in the existingdirection of the thickness-increased direction.

[0083] On the outer side of the first thickness-increased portion 3,there is provided a first seal line SL1 in a manner to endlesslyencircle the combustion chamber opening 2 along the peripheral portionof the combustion chamber opening 2. On the outer side of the first sealline SL1, a plurality of cooling water holes 8 are arranged along theperipheral portion of each combustion chamber 2.

[0084] On the outer side of the plurality of the cooling water holes 8,a second seal line SL2 is provided in a manner to encircle all of thecooling water holes 8. The second seal line SL2 is so arranged thatthere are no other holes than the cooling water holes 8 in the area ofthe base plate 20 which is located between the first seal line SL1 andthe second seal line SL2.

[0085] On the outer side of the seal line SL2, the bolt holes 6 arelocated. An oil hole is denoted by reference numeral 7.

[0086] A third seal line SL3 is provided in a manner to encircle thebolt holes 6 and the oil hole 7.

[0087] The seal lines SL1 to SL3 are integrated into a single commonseal line where they run adjacent to one another.

[0088] A second thickness-increased portion 9 is formed by upwardlyfolding up the outer peripheral edge of the base plate 20 at some partsof the base plate 20. The height of the second thickness-increasedportion 9 is arranged to be a little lower than the smallest height ofthe first thickness-increased portion 3 by forging.

[0089] As shown in FIGS. 2 and 3, a bead BD is formed along the seallines SL1 to SL3. As shown in FIGS. 2 and 3, the bead BD in thisembodiment is formed as a composite of a metal bead 4 or 5 and a rubberbead.

[0090] The metal beads 4, 5 in this embodiment are full beads formed bybending the base plate 20 so as to protrude on only one surface side(top surface side) of the base plate 20 and the beads are arranged to behigher than the first thickness-increased portion 3. Therefore, when thebeads are elastically deformed in the through-thickness direction, asealing pressure can be generated.

[0091] The above-mentioned rubber bead comprises elastic sealingmaterial parts 11 a, 11 b, 13 a, 13 b fixed to the surface of the baseplate 20 on the convex portion side of the metal beads 4, 5, and elasticsealing material parts 10 and 12 filled in the concave portion on thereverse side of the convex portion. The elastic sealing material parts11 a, 11 b, 13 a, 13 b, and 10, 12 may be formed by acorrosion-resistant, elastic material, e.g., a rubber material, such asfluororubber, NBR, silicon rubber, or a resin material.

[0092] The elastic sealing material parts 11 a, 11 b, 13 a, 13 b fixedto the convex portion side of the metal beads 4, 5 are fixed to thesurface of the base plate 20 in a manner to cover at least both sidesacross the width of the metal beads 4, 5. The height of the elasticsealing material parts 11 a, 11 b, 13 a, 13 b fixed to the convexportion side of the metal beads 4, 5 is made equal or substantiallyequal to the height of the convex portion of the metal beads, and thetop surface is made substantially parallel with the flat surface of thebase plate 20. The height of the elastic sealing material parts 11 a, 11b, 13 a, 13 b may be a little higher than the height of the convexportion of the metal beads 4, 5. Note, however, that the above-mentionedheight of the elastic sealing material parts must be a height such thatthe compression-deformed amount regulated by the height of the firstthickness-increased portion 3 is not more than 35% (the knowncompression-deformed amount of a specific material, which does not giverise to buckling).

[0093] On the other hand, the amount of the elastic sealing materialparts 10 and 12 filled in the concave portions of the metal beads 4, 5is made substantially equal to the capacities of the concave portionsand their back surface is made substantially flush with the flat backsurface of the base plate 20.

[0094] Description will next be made of the operation and the effect,etc. of the metallic gasket mentioned above.

[0095] When a metallic gasket 1 structured as described is disposedbetween the opposing joint surfaces of a cylinder block and a cylinderhead and fastened with clamping bolts, the elastic sealing materialparts 11 a, 11 b, 13 a, 13 b and the elastic sealing material parts 10,12 that constitute the rubber beads are compressed and deformed in thethrough-thickness direction in cooperation with the metal beads 4, 5,and at the end of fastening, the largest surface pressure concentrateson and the largest load acts on the first thickness-increased portion 3due to a difference in thickness between the first thickness-increasedportion 3 with the largest thickness of the base plate 2 and theremaining portions.

[0096] Therefore, a combustion gas at the highest pressure can be sealedby the first thickness-increased portion 3 pressed against the jointsurface. On the outer side of the first thickness-increased portion 3,an area seal is applied by an elastic resilience of the beads BD (metalbeads 4, 5 and rubber beads) formed along the first and second seallines SL1 and SL2 as a shield against cooling water seeping out betweenthe seal lines.

[0097] And, as the largest compression-deformed amount of the beads BDis regulated by the first thickness-increased portion 3, a largest everspace, more specifically, a gap space SP corresponding to the clearanceof a piece of the whole base plate 20 is formed between the first sealline SL1 and the second seal line SL2, thereby increasing the coolingeffects of the metallic gasket 1. In other words, as a water pumppressure-feeds the cooling water into the gap space SP from a coolingwater hole 8, and the cooling water, while flowing, absorbs the heatgenerated by engine operation and transmitted from the engine, andsimultaneously cools the gasket 1, thus preventing the rubber beads ofthe gasket from deteriorating by heat.

[0098] At this time, the beads BD in this embodiment seal the jointsurfaces by a composite spring force of the metal beads 4, 5 and therubber beads, and since the sealing areas of the beads to contact theupper and lower joint surfaces are formed by the elastic sealingmaterial parts 11 a, 11 b, 13 a, 13 b and 10, 12, a small gasket factorcan be set and the sealing can be applied by a low surface pressure, andeven if the compression-deformed amount is regulated to increase theamount of the gap space SP as described above, no problem arises.

[0099] Because the upper and lower sealing areas are the sealing areasby the elastic sealing material parts 11 a, 11 b, 13 a-13 b and 120, 12,if there are blowholes or the like on the joint surfaces, a sufficientsealing against water leakage can be obtained. Further, the rubber beadsare capable of sufficiently sealing the surface processing roughness orthe flaws that occur in transit.

[0100] As mentioned above, since a small gasket factor can be set forthe beads BD, no problem occurs if the base plate 20 is formed bylow-hardness less-expensive soft steel plate. The elastic sealingmaterial parts 11 a, 11 b, 13 a, 13 b and 10, 12 are used only on theupper and lower portions of the bead lines required for sealing, andtherefore the consumed amount is small.

[0101] The metal beads 4, 5 are required only slightly higher than theheight of the first thickness-increased portion 3, and the height of therubber beads is set so as to be equal or slightly higher than the heightof the metal beads 4, 5 in designing the mold, and therefore theprocessing accuracy is stable. If the height of the metal beads is 30%higher than the first thickness-increased portion, the elastic sealingmaterial does not suffer deformation fracture, generated load is acomposite force of the metal beads of soft steel and the soft rubberbeads and is therefore not strong, and there is not such a large loss ofload as to affects the sealing against the combustion gas pressure.

[0102] By varying the thickness in the circumferential direction of thefirst thickness-increased portion 3, the sealing pressure is equalizedand consequently the fastening force of the bolts can be utilizedefficiently. As a result of the pressure being equalized in thecircumferential direction in the peripheral portion of the combustionchamber opening 2, the pressure of the joint surface in contact with thefirst thickness-increased portion 3 on the opening edge of thecombustion chamber (bore) is equalized in the circumferential direction,and therefore the roundness of the combustion chamber bore is preventedfrom being impaired by the imbalance of the sealing pressure at thefirst thickness-increased portion 3. The impairment of the roundness ofthe combustion chamber (bore) leads to increases in power loss and oilconsumption. Between the first and second thickness-increased portions3, 9 which receive a large proportion of the bolt fastening force, bymaking the second thickness-increased portion 9 relatively lower inthickness, the largest load may be applied to the firstthickness-increased portion 3 to thereby generate a high sealingpressure.

[0103] Since the base plate 20 is formed by soft steel plate of lowhardness, it is easy to form the first thickness-increased portion 3 andthe second thickness-increased portion 9 by bending.

[0104] The variation of the height of the first thickness-increasedportion 3 in the circumferential direction may be adjusted by forging,or as shown in FIG. 4, may be adjusted by inserting a shim plate 14 ainto the folded portion. When the shim plate 14 a is inserted in thefolded portion along the whole periphery of the firstthickness-increased portion 3, where there is the smallest thicknessportion of the shim plate 14 a, the first thickness-increased portion 3is at its smallest thickness. As a result, the height of the secondthickness-increased portion 9 can be made lower than the firstthickness-increased portion 3 without forging. In other words, settingthe shim plate 14 a in the first thickness-increased portion 3 obviatesthe need to perform the forging to the second thickness-increasedportion 9. The shim plate 14 a set in the first thickness-increasedportion 3 increases the height of the first thickness-increased portion3 by its thickness, and therefore the gap space SP in which coolingwater circulates can be made wider in proportion to the thickness of theshim plate 14 a, thus improving the cooling effects.

[0105] At this time, as shown in FIG. 5, a leaf spring 14 b elasticallydeformable in the through-thickness direction may be inserted as theshim plate 14 a into the first thickness-increased portion 3. In thiscase, in addition to the above-mentioned effect, the surface pressure inthe circumferential direction of the first thickness-increased portion 3is equalized more readily by the elastic force of the leaf spring 14 b,and by this added spring of the first thickness-increased portion 3, thefirst thickness-increased portion 3 can follow after the thermaldeformation that occurs during engine operations and consequently thesurface pressure equalization takes places in the firstthickness-increased portion 3 in a manner to follow the thermaldeformation.

[0106] In this embodiment, description has been made of the metal beads4, 5 as full beads, but as shown in FIG. 6, in the bead BD formed alongthe second seal line SL2, the metal bead 5 may be formed by a half bead.In other words, in the areas where an available seal width is too narrowto provide a full-bead 5, the metal bead 5 may be formed as a half beadto suit the narrow seal width.

[0107] In this embodiment, description has been made of thethickness-increased portion formed by folding back the base plate, butthis is not intended to give a definition of limits of the invention.For example, as shown in FIG. 7, the second thickness-increased portion9 may be formed by welding a thin plate thinner than the base plate 20to the outer peripheral edge, thus obviating the necessity of forgingmentioned above. Or, the second thickness-increased portion may beformed by folding back the peripheral portion of each bolt hole.

[0108] The sealing surface pressure by the metal beads 4, 5 may beequalized by partly varying at least one of the protruding height andthe width of the beads in their extending direction. For example, theprotrusions of the beads are made relatively low or the bead width ismade relatively narrow in the vicinity of bolts. By equalizing thesealing pressure, the gasket can be sealed with high accuracy.

[0109] To the base plate part between the two beads BD along SL1 andSL2, a corrosion-resistant thin film may be fixed, which preventsrusting on the surface of the base plate which always contact water.

[0110] A second embodiment of the present invention will be describedwith reference to the drawings.

[0111] The basic structure of this second embodiment is the same as thatof the first embodiment, but slightly differs in the structure of thebead from the first embodiment.

[0112] Beads are formed along the seal lines SL1 and SL2.

[0113] As shown in FIGS. 8 and 9, the bead BD according to thisembodiment is a composite bead formed by a base-plate bead 6 as a fullbead and rubber beads 8, 10.

[0114] The base-plate bead 6 is formed by bending the base plate in thethrough-thickness direction and the base-plate bead 6 is formed convexthat is higher than the height of the thickness-increased portion 16.

[0115] The rubber bead comprises a first elastic sealing material part10 filled in the concave portion of the base-plate bead 6, and a secondelastic sealing material part 8 fixed to the convex portion side of thebase-plate bead.

[0116] The first elastic sealing material part 10 is arranged such thatthe under surface of it is flat and flush with the under surface of thebase plate 2. Approximately in the center of the width direction of thebead and on the under surface of the bead, a convex protrusion 11 isformed along the seal lines SL1 and SL2.

[0117] The second elastic sealing material part 8 is formed with a widthslightly wider than the width of the base-plate bead 6 and on thesurface of the convex portion of the bead and on the flat surfacecontinuous to the convex portion. The second elastic sealing materialpart 8 is designed so that its height is almost equal to the height ofthe base-plate bead 6 and the surface (the top surface) is substantiallyflat.

[0118] The width of the second elastic sealing material part 8 ispreferably not more than 1.5 times the width of the base-plate bead 6.If the width is increased excessively, load increases excessively. Theheight of the elastic sealing material part 8 is preferably in the rangeof 0.9 to 1.1 times the height of the base-plate bead 6.

[0119] The number and the kinds of holes, such as the bolt holes 4formed in the base plate 2, and the location of the seal lines SL1 andSL2 naturally differ with the kind of a cylinder block and a cylinderhead between which the metallic gasket 1 is disposed.

[0120] The metallic gasket 1 structured as described is set in placewhen it is disposed between the joint surfaces of the cylinder block andthe cylinder head of an engine and fastened with clamping bolts. Thebeads are deformed by the fastening force of the clamping bolts and arequired sealing pressure is generated along the seal lines to therebyseal oil, water and so on.

[0121] When the gasket is fastened, the thickness-increased portions 16provided at the peripheral end portion of the combustion chamber opening3 serve to limit the compression-deformed amount of the beads, a highsurface pressure occurs at the thickness-increased portions 16, so thatthe thickness-increased portion 16 seals a combustion gas at hightemperature and high pressure.

[0122] When no coating is applied to the surface of thethickness-increased portion 16 to supply the gasket at a low price, thethickness-increased portion 16 of the gasket comes into metal-to-metalcontact with the machined surfaces (joint surfaces) of the engine, andconsequently there is a tool-mark irregularity of 3 to 6 microns on themachined surfaces.

[0123] The explosion pressure by engine operation is not aconstantly-applied pressure but a pulsating pressure; therefore, thereis some pressure leakage from the thickness-increased portion 16 to theouter periphery side. However, the pressure is sealed by the bead BD onthe outer side of the thickness-increased portion 16.

[0124] The bead BD according to this embodiment is so structured as togenerate a required sealing pressure by a composite spring of thebase-plate bead 6 and the rubber bead produced when they are compressedand deformed, and this composite structure makes it possible to reducethe hardness of the base plate 2 that forms the base-plate bead 6. Thebeads contact the upper and lower joint surfaces at the flat surfaces ofthe compressed and deformed elastic sealing material parts 8 and 10, andthe soft elastic sealing material parts 8 and 10 come into tight contactwith the joint surfaces, closing any small spaces of the tool marks,thereby sealing the combustion gas that leaks from thethickness-increased portion 16 under pulsating pressure mentioned above.

[0125] In a gasket of a structure that an elastic sealing material isfilled only in the concave portion of the base-plate bead 6, when theelastic sealing material 10 is compressed and deformed, an externalforce is generated to deform the base-plate bead 6 and the flat portionon each side continuous to the base-plate bead 6 in such a manner thatthey warp upward. The lower the hardness of the base plate 2 is made toinhibit fatigue failure of the base-plate bead 6 and hold down the costof the base plate 2, the more conspicuous the deformation, such asupward warp is likely to become. However, in this embodiment, the secondelastic sealing material 8 is provided also on the convex portion sideand the second elastic sealing material 8 is deformed to preventdeformation of the base-plate bead 6 and the base plate 2, therebypreventing the deterioration of the seal performance by the firstelastic sealing material 10 in the concave portion.

[0126] In the filling of the first elastic sealing material 10, thecenter portion of it is likely to cave in a little in a transition fromhigh temperature to open cooling. In this embodiment, protrusions 11 and9 are formed on the above center portion, even when the gasket isadopted in an engine whose fastening axial tension is weak, a stableseal performance can be secured at low lost in the region on the outerside of the combustion chamber opening 3. After the bolts are fastened,the protrusions 11 and 9 are in a crushed and flattened state.

[0127] No fastening problem arises in the vicinity of bolts 4 is free ofas long as the bolts are fastened properly. However, the oil holes 5 andthe chain chamber hole 17 are in an improperly fastened state becausethey are remote from clamping bolts. As the engine is subjected torepeated thermal cycles as many times as it is used, the fastening axialtension decreases to some extent. The gasket is deformed by heat duringengine operation, thus aggravating the sealing condition.

[0128] In order to implement a complete seal under those adverseconditions, in the prior art, in the bead structure having the elasticsealing material filled in the concave portion of the base-plate bead,if the hardness of the base plate 2 is increased, the spring force isincreased, but the bead may suffer fatigue failure by vibrationamplitude, and it is not desirable to increase the hardness so much; onthe other hand, if the hardness of the base-plate bead 6 is decreased,deformation mentioned above will occur, resulting in a decrease in thespring force. To make up for this shortcoming, in this embodiment, asdescribed above, in addition to the first elastic sealing material 10filled in the concave portion of the base-plate bead 6, the secondelastic sealing material 8 is formed on the convex portion on thereverse side of the concave portion, and the second elastic sealingmaterial 8, structured such that its width is wider than the width ofthe bead and its height is substantially the same height of thebase-plate bead 6, serves to prevent deformation of the base plate 2 andthe base-plate bead 6.

[0129] As the hardness of the base plate 2 is lowered, the spring forceis made low, but because the first elastic sealing material 8 is formed,on the convex portion, with a height equal to the height of thebase-plate bead 6 to thereby regulate the deformation by the elasticsealing material 10 filled in the concave portion, with the result thatthe BD bead is provided with a spring force equal to or greater than aspring force by a structure that uses the base plate 2 of ahigh-hardness material.

[0130] Further, when the elastic sealing material 10 is formed bymolding, the concave portion side of the base-plate bead 6 is processedso as to be flush with the flat surface of the base plate 2. Duringmolding, the sealing material 10 expands thermally by high temperature,but when it is open-cooled, the central portion of the rubber large inthickness shrinks by an amount corresponding to thermal expansion, andcaves in slightly, and in the portions, away from a clamping bolt, whichare not fastened properly and overhang, the surface pressure maydecrease, leaving chances of pressure leak.

[0131] As countermeasures, according to the invention in this patentapplication, as shown in FIG. 8, a small protrusion 11 is formed in themiddle of the surface of the elastic sealing material 10 in the concaveportion of the base plate 6, the bead is deformed without increasing thefastening load so much, and when the surface pressure decreases, theprotrusion 11 formed on the surface of the first elastic sealingmaterial 10 bulges and deforms concurrently. Though small in terms ofarea, the protrusion generates a high surface pressure, and serves toapply a complete seal. In other words, located in a position away fromthe clamping bolt to the outer circumference side, the surface pressuretends to become relatively small, the elastic sealing material on bothsurfaces of the base-plate bead 6 is normally pressed to the opposedjoint surfaces to seal them by the compressed and deformation of thebead by the fastening load. At this time, the protrusion 11 formed onthe elastic sealing material 10 on the concave portion side is deformedin a manner to be pushed into the concave portion, adapts itself to theflat surface of the joint surface, and becomes substantially flush withthe flat surface (underside) of the base plate 2.

[0132] When, from this steady state, the clearance between the opposedjoint surfaces at the bead position increases by vibration, for example,the surface pressure temporarily decreases, the compression-deformedamount of the bead decreases, thus reducing the sealing pressure. At theelastic sealing material 10 on the concave portion side, according to anincrease in the clearance, the protrusion 11 automatically bulges tosecurely retain contact with the opposite joint surface and has thecontact surface decreased, and can maintain the seal condition by anincrease in the surface pressure by the protrusion. As the clearancedecreases, the steady state is restored.

[0133] In the foregoing, description has been made of a case where thesurface pressure decreases with changes in the clearance between theopposed joint surfaces. Even when the clearance between the opposedjoint surfaces remain unchanged or even when the spring force decreaseswith deterioration with time and the surface pressure becomes smaller,as described above, because load concentrates on the protrusion 11 asthe surface pressure decreases (the protrusions 11 and 9 do notnecessarily bulge in this case), the surface pressure rises at theposition of the protrusion 11, making it possible to maintain aspecified sealing pressure.

[0134] When the change in the gap at the bead position between the jointsurfaces is large, it is preferable to form a protrusion 9 also on theelastic sealing material on the convex portion of the base-plate bead 6as shown in FIG. 10.

[0135] The protrusions 11, 9 arranged in the bead-width direction arenot limited to one, and may be two or more as shown in FIGS. 11 to 13.When two or more protrusions are provided, the height of the protrusions11, 9 may be made different. The magnitude of the protrusions may alsobe different. When a plurality of protrusions are formed, load ofsurface pressure can be alleviated, or if the surface pressuredecreases, a labyrinth effect may be obtained by the plurality ofprotrusions 11, 9 or the de facto increase of the seal lines SL providesan effect of a stable sealing property for an extended period of time.

[0136] Further, with regard to the plurality of protrusions 11, 9, bymaking variations in the size or shape (the area unit length in alongitudinal sectional profile or a plan view) of the protrusions 11, 9to seek optimization of the protrusions 11, 8 as shown in FIGS. 31 to34, it is possible to enlarge the above-mentioned effects. In otherwords, when providing two or more protrusions in parallel widthwise, itis preferable to make the height of the protrusions 11, 9 relatively lowor reduce the area per unit length on the higher surface pressure side.

[0137] With regard to a single-line protrusion 11, 9 extending along theseal line, it is possible to change the height or shape of theprotrusion 11, 9 according to the surface pressure at the location ofthe protrusion 11, 9. In other words, in the areas where the surfacepressure is relatively smaller, the height and the width of theprotrusion 11, 9 may be increased.

[0138] The protrusions 11, 9 may be formed continuously along the wholelength of the seal lines SL1 and SL2 or intermittently at specifiedintervals.

[0139] When the protrusions 11, 9 are formed partly on the seal linesSL1, SL2, they should be formed at positions that are far from the bolthole and at relatively low surface pressure or at parts where changes inthe clearance between the opposed joint surfaces are relatively large(the amplitude of surface pressure change is relatively large).

[0140] In this embodiment, description has been made of the base-platebead 6 as a full bead, but this embodiment is applicable when thebase-plate bead 6 is a half bead in a stepped structure. Morespecifically, as shown in FIGS. 18 and 19, a second elastic sealingmaterial 12 is fixed to the convex portion (the portion rising from theflat part of the base plate) of the base-plate bead 6 in a stepped form,a first elastic sealing material 14 is applied to the concave portion onthe reverse side of the convex portion, and then protrusions 13, 15 areformed at the thick portions. The operation and the effect are the sameas in the above-mentioned embodiment.

[0141] In the bead BD in the vicinity of the thickness-increased portion1, the second elastic sealing material need not necessarily be attachedto both sloped sides of the convex portion as shown in FIG. 20. In otherwords, receiving a relatively high surface pressure and having a strongforce to constrain the base plate, the thickness-increased portion 16inhibits the base plate from being deformed. This applies to theportions in the vicinity of clamping bolts.

[0142] The height of the protrusions 11, 9 should be designed such thatthe deformation ratio is not more than 25% when the protrusions aredeformed to reach the thickness of the thickness-increased portion 16,regardless of the shape of protrusions.

[0143] In the above example, description has been made of a metallicgasket having a single base plate. In a metallic gasket, a plurality ofbase plates, each having the above-mentioned structure, may be stackedone over another according to the space between the joint surfaces. Inthis case, the base plates need not necessarily be stacked such that theconvex portions of the base-plate beads are arranged face-to-face witheach other as in prior art.

[0144] The other aspects of the structure, the operation and the effectare the same as in the above-mentioned embodiments.

[0145] Industrial Applicability

[0146] As has been described, by adopting the present invention, theprocessing accuracy of the metal beads can be improved and the coolingeffects can be increased on the metallic gasket itself and the jointsurfaces between which the metallic gasket is sandwiched.

1. A metallic gasket comprising a base plate made of a thin metal plate, said base plate having at least a combustion chamber opening and a cooling water hole, and having a first thickness-increased portion made of metal and increased in thickness and encircling a peripheral edge of said combustion chamber opening, a first bead formed on the outer side of said first thickness-increased portion of said base plate in a manner to endlessly encircle said combustion chamber opening, and a second bead formed on the outer side of said first bead in a manner to endlessly encircle said combustion chamber opening and said cooling water hole, wherein in a region of said base plate between said first bead and said second bead, there are no holes other than said cooling water hole, and each of said first and second beads is a composite bead of a metal bead and a rubber bead, wherein said metal bead is formed only on one surface side of said base plate by bending said base plate in a through-thickness direction to create a convex portion higher than the height of said first thickness-increased portion, wherein said rubber bead is formed of an elastic sealing material fixed to said convex portion side surface of said metal bead and filled in a concave portion on the reverse side of said convex portion and said rubber bead is compressed and deformed in the through-thickness direction in cooperation with deformation of said metal bead, and wherein said elastic sealing material on the surface of said convex portion side is fixed at least to the surface of said convex portion of said metal bead and is arranged to have a height equal or substantially equal to the height of said metal bead.
 2. A metallic gasket according to claim 1, wherein a second thickness-increased portion is provided at an outer peripheral edge of said base plate.
 3. A metallic gasket according to claim 2, wherein to equalize said surface pressure when said gasket is sandwiched between said joint surfaces, the height of said first thickness-increased portion is varied partly and the height of said second thickness-increased portion is lower than the lowest height of said first thickness-increased portion.
 4. A metallic gasket according to claim 3, wherein said first thickness-increased portion is formed by folding back a peripheral edge on said combustion chamber opening side of said base plate, and a shim is fitted into said folded portion to thereby adjust the height of said first thickness-increased portion.
 5. A metallic gasket according to one of claims 1 to 4, wherein said first thickness-increased portion is formed by folding back the peripheral end on said combustion chamber opening side of said base plate, and a leaf spring for spring action in the through-thickness direction is inserted in said folded portion.
 6. A metallic gasket according to one of claims 1 to 4, wherein by partly varying at least one of a height of said protrusion and a width of said beads in the extending direction thereof, said sealing surface pressure by said beads is equalized in an extending direction thereof.
 7. A metallic gasket according to one of claims 1 to 4, wherein a thin corrosion-resistant film is fixed to that portion of said base plate located between said first bead and said second bead and at least on the surface of said convex portion side of said metal beads on said base plate.
 8. A metallic gasket according to one of claims 1 to 4, wherein one or not less than two seal lines are arranged on at least either on one of the surface of said elastic sealing material fixed to the surface of said convex portion side and the surface of said elastic sealing material filled in said concave portion, said sealing material being used to constitute said rubber beads.
 9. A metallic gasket according to one of claims 1 to 4, wherein one line or not less than two lines of protrusions are provided where the sealing pressure is relatively low on at least one of the surface of said elastic sealing material fixed to the surface of said convex portion side and the surface of said sealing material filled in said concave portion of said base plate, said sealing material being used to constitute said rubber beads.
 10. A metallic gasket according to claim 8, wherein in the above-mentioned lines of protrusions, at least one of the height of said protrusion and the width in the extending direction thereof is varied according to said sealing pressure at formed positions said protrusions, and at least one of the height of said protrusion and the width is set at a larger value where said sealing pressure is lower.
 11. A metallic gasket according to claim 8, wherein a plurality of protrusions are provided on at least one of the surface of elastic sealing material fixed to the surface of said convex portion side and the surface of said elastic sealing material filled in said concave portion of said beads, and in said plurality of protrusions, at least one of an area per height of protrusion and a unit length is varied according to said sealing pressure at formed positions of protrusions.
 12. A metallic gasket according to one of claims 8, 10 and 11, wherein a plurality of base plates are stacked in a multilayered structure. 